Electric circuit breaker



Jan.'17, 1939. E, B, MERRIAM `ELECTRIC CIRCUIT BREAKER Filed Feb. l2, 1938 OIL LEVEL Inventor. Ezra B. MerPam,

His ttorney.

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Patented Jan. 17, 1939 UNITED STATES PATENT OFFICE Ezra B. Merriam, New

Haven, Conn., assigner to General Electric Company, a corporation of New York Application February 12, 1938, Serial No. 190,263

3 Claims.

My invention relates to electric circuit breakers of the explosion chamber or oil blast type, and has for its principal object the provision of an improved circuit breaker that is elective to limit extension of the arc due to oil blast upon opening of the circuit,

The use in oil circuit breakers of means for preventing excessive extension of the arc formed upon opening of the circuit is known, and devices responsive, for example, to magnetic, arc pressure, and other conditions have been proposed for this purpose. As is well known, the pressure generated within an oil circuit breaker housing during arc interruption is dependent, inter alia on the length of the arc, and undue stretching or looping of the arc is therefore undesirable for that reason. Devices heretofore proposed, however, are generally somewhat complicated, particularly Where additional moving parts are involved, and so increase the cost both of maintenance and of equipment itself.

In accordance with a specific application of my invention to a well-known form of explosion chamber, means are provided for preventing arc extension, such as by looping of the arc into the movable tubular contact under influence of the oil blast.

My invention Will be more fully set forth in the following description referring to the accompanying drawing, and the features of novelty which characterize my invention Will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Referring to the drawing, the single figure thereof is an elevational View, partly in section, of the relatively movable contact structure of an oil circuit breaker of the explosion chamber type.

A single pole of a Well-known form of oil circuit breaker is illustrated by way of example, the relatively movable contact structure comprising a stationary housing or explosion: chamber l coacting with a movable tubular contact 2. The stationary contact structure can be of any suitable form, such as for example, a single break explosion chamber, or a double break form Wherein a pressure-generating break is utilized in a. manner well known in the art for generating oil blast pressure.

As shown the contact structure is immersed in a suitable arc-extinguishing liquid such as oil so that the explosion chamber I is completely filled with oil. It shall be understood that the term oil as used in the present specification -and claims is intended to comprehend any suitable arc-extinguishing liquid. The chamber I (Cl. 20o-150) is mounted at the lower end of the lead-in bushing 3 insulating the circuit conductor 4, and encloses suitable fixed contact structure 5.

In the operation of this general type of circuit breaker the movable tubular contact 2 is elevated from the open circuit position shown to engage the fixed contact 5 through the throat or oil blast opening I of the explosion chamber. The circuit-opening operation is effected by lowering the contact 2, thereby forming an arc between the separated contacts 2 and 5, which in turn generates pressure within the explosion chamber due to vaporization of the oil. This pressure causes an oil blast to traverse the arc even before the contact 2 clears the throat l by reason of the tube vent 2 As the oil converges radially on the arc in exhausting through the vent 2 of the tubular contact 2, the oil blast tends to extend or loop the arc into the tubular contact. It was generally believed, however, that the arc did not extend an appreciable distance into the conducting tube but was instead quickly short circuited by the Walls thereof as it was looped into the tube.

I have found instead that the arc length and, consequently, the arc pressure can be considerably decreased by lining the inner Walls of the tubular contact with a suitable arc-resisting insulating material. Contrary to general belief I have also found that the are is often driven an appreciable and unexpected distance into the tubular contact, in certain cases as much as 8 inches, with the result that unnecessarily long arcs are drawn during interruption.

Even though the arc may be interrupted when the tubular contact 2 finally clears the throat I by reason of the main oil blast from the chamber, it is generally highly desirable to interrupt the arc before it has been drawn to an appreciable length. In other Words, it is desirable that the arc be interrupted while the tubular contact is still in the throat passage, or even before it reaches said passage.

For the purpose of eliminating extension of the arc by looping into the tubular contact, and for facilitating interruption of the arc Within a small part of the opening stroke, I provide insulating means such as for example an insulating sleeve 6 of strong arc-resisting material for lining the interior of the tubular Contact 2. As shown the insulating lining 6 extends only to the removable arcing tip 'l which is of course of a suitable arc-resisting contact material.

Accordingly, when the arc upon opening of the circuit is driven by the oil blast into the tubular contact, the root or crater of the arc does not extend beyond the arcing tip 1. Further extension of the arc by bowing or looping simply results in automatic short circuiting of the arc by the opposite conducting walls of the arcing tip since the arc crater cannot move down into the tube. It therefore follows that the arc drawn between the contacts 2 and 5 while subject to the radial oil blast from the chamber l is maintained substantially at its minimum length notwithstanding the tendency of the oil blast to extend the arc within the tubular contact. With the arc so limited in length, arc interruption by the oil blast is also facilitated since the oil velocity at the arcing tip 'l is comparatively high and furthermore is not greatly reduced by arc counterpressure in the tube passage 2'.

It should be understood that my invention is not limited to specific details of construction and arrangement thereof herein illustrated, and that changes and modifications may occur to one skilled in the art Without' departing from the spirit of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

Y l. An electric circuit breaker of the uid blast type comprising relatively movable contacts, an extinguishing chamber for directing an arc-extinguishing fluid blast between the contacts upon opening of the circuits, one of said contacts being tubular in form for receiving part of the blast and disposed with respect to said chamber so that the blast tends to shift the arc root from the contact tip of said tubular contact into the tube and along the inner conducting surface thereof to increase the length of said arc, and means for insulating the interior of said'tubular Contact kfor precluding said extension of the arc.

2. An electric oil circuit breaker comprising fixed Contact structure including an oil immersed explosion chamber, a movable tubular contact coacting therewith arranged so that an oil blast is directed through the arc formed upon opening of the circuit into said tubular contact, and insulating means disposed withinrsaid tubular contact for preventing appreciable movement of the arc root into said tubular contact coincident with the aforesaid oil blast.

3. An electric oil circuit breaker comprising fixed contact structure including an oil immersed explosion chamber, a coacting tubular contact movable through a blast exhaust opening of said chamber, separation of the fixed and movable contacts within said chamber being accompanied by arc-generated pressure causing a radial oil blast through the arc and into said tubular contact, said oil blast tending to shift the arc root from the tubularv contact tip into the tube and along the inner conducting surface thereof to increase the length of said arc, and an insulating lining for said tubular contact for precluding said extension of the arc.

EZRA B. MERRIAM. 

